Making white-corrected positives for the production of printing plates



April 19, 1938.

MAKING WHITE CORRECTED POSITIVES FOR THE PRODUCTION OF PRINTING PLATES w. J. WILKINSON 2,114,325

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tive in which the areas representing white are Patented Apr. 319, 193% UNITED STATES ZM ZQBZS MAKING WHITE-CORRECTED POSITIVES FOR THE PRODUCTION OF PRINTING PLATES William J. Wilkinson, Eastchester, N. Y; assignor to Miehle Printing Press & Manufacturing Company, illiicago, 111., a corporation of Elinois Application January 12, 1935, Serial No. 1,487

3 ohm This invention relates to a process and means for producing color separation positives suitable for use in the photographic production ofprinting plates.

In the preparation of color separation positives for the above purpose, certain dificulties are involved in the reproduction of the white areas because the portions of the negative representing such areas are usually not sufficiently dense or opaque to entirely prevent the passage of light when the positive is printed therefrom. This dfiiculty may, in some instances, be overcome by manually painting or opaquing in the areas of the negatives representing the whites. In color printing, however, where three or more color separation negatives are required, it is extremely difficult, and many times impossible, to manually correct the various negatives with the accuracy required to obtain correct registration.

An object of the present invention is to provide a simple, cheap and dependable means for eliminating the above difficulties.

Another object is to simplify the correction of the areas in color separation negatives representing white in the subject.

Another object is to provide a method and means for assuring accurate registration of the corrected color separation positives.

Another object is to provide a system for the above purpose which is readily applicable to color printing involving any number of color separation pos ives.

Another object is to provide a simplified means for photographically producing color printing plates.

Various other objects and advantages will be apparent as the nature of the invention is more fully disclosed.

A feature of the present invention resides in photographically producing the pure white areas in the positive. In one form of the invention this is accomplished by producing a block-out negaopaque and all areas representing tones other than white are transparent. This block-out neg ative is used as an overlay for the various color separation negatives in turn so as to completely block'out the white areas, and the color separa-- tion positives are then made by photographing through each color separation negative and the single overlay.

Another feature resides in the means for producing the block-out negative. In one embodiment this is obtained by printing a positive from one of the color separation negatives and manuallypainting or opaquing in on the positive all areas representing tone values other than white. This positive is then printed on film to produce the block-out negative inwhich the areas representing the whites are opaque but the remaining 5 areas are entirely clear and transparent.

Although the novel features which are behaved to be characteristic of this invention will be more particularlypointed out in the claims appended hereto, the invention itself will be better understood by referring to the following description taken in connection with the accompanying drawing forming a part thereof, in which the single figure constitutes a flow-sheet of the new procedure.

More specifically, in carrying out the present process a series of color separation negatives corresponding to the individual colors required to reproduce the original composite coloring are made in the usual manner from the colored subject to be reproduced. These separation negatives are in general diagrammatically illustrated in the drawing as a negative i9 having a clear portion H representing all colored areas of the subject, -a darker portion 52 representing the areas of medium tones and a dark portion i3 representing all white areas of the original subject. The portion l3 representing the white areas, however, is gray but is not entirely opaque. For photographic reasons it would be diilicult, if not impossible, to make such portions entirely opaque without, at the same time, losing certain of the other desired tones. Obviously, if a positiveis printed from the above separation negative the gray portion l3 will transmit some light and the corresponding areas on the positive will not be entirely clear or transparent, or, in the case of a half-tone print, will not be entirely free from dots.

In order to correctly reproduce white areas on the-positive a block-out negative is made which is adapted to completely block out portions of the negative representing such areas. For this purpose one of the color separation negatives is selected," preferably the one having the greatest detail, and a contact print is made therefrom on a contrasty plate. This positive is illustrated in the drawing as a positive l4, having a. black area (5, an area It of medium tone and a light area'll corresponding to the portions ll, l2 and I3 respectively of the negative 10. The light area I! represents the whites of the subject, the other areas l5 and l5 representing tones other than white. 4/ All of the ys values except white on this block-out negative I9, in which the areas 20 repnegatives.

resenting the whites are opaque and the remainder 2| is entirely clear and transparent.

This block-out negative I9 is now used in turn in conjunction with each of the original separation negatives I to produce a set of corrected half-tone positives which are adapted to be used in the photographic production of the printing plates. For this purpose, the block-out negative I9 is used as an overlay for each color separation negative I0 and a positive is made by photographing through the separation negative Ifiv and the negative overlay 89 either in a vacuum printing frame or in a camera. This positive will accurately represent all tones of the subject and will be clear or transparent in the white areas.

Such a positive is shown in the drawing having a white area 25, a medium-tones area 26 and a dark or black area 2?. This positive may be used for the production of a half -tone negative or positive suitable for transfer to the printing plate. If desired, the half-tone positive may be made directly from the separation negative I81 and the overlay I9 by photographing the same through a half-tone screen by-light transmitted through said negatives. In such a positive all of the tones are represented by the usual half-tone dots, but the whites are entirely free from dots. This half-tone positive may be used for the photographic production of a printing plate for use in any standard printing process, such as the offset process, or a half-tone negative may be made therefrom and used to produce a half-tone cut for relief printing.

The above process is repeated with each of the color separation negatives, using the same blockout negative I9 with each of the color separation Since the block-out negative is made photographically from one of the separation negatives and is utilized for the correction of each of the negatives, accurate registration of the white areas is assured. Furthermore; the process may be quickly and cheaply carried out inasmuch as the necessity for highly skilled manipulation is largely eliminated.

It is obvious that this color correction process is applicable to the production of various types of printing plates and is not limited to use with half-tone positives. ,It may be used for the production of either a corrected positive or negative, with. or without a lined screen. It has been lescribedin connection with the production of a half-tone positive for use in off-set printing merely by way of illustration.

It is also obvious that the correction process is applicable to one color printing or to variouscases where a plurality of negatives are to be corrected. Color printing has been set forth only as an example.

Although certain specific embodiments of the invention have been set forth herein, the invention is not to be restricted thereto, but is only to be limited in accordance with the following claims when interpreted in view of the prior art.

I claim: i

1. The process of making a white-corrected positive from a negative of the original subject, which comprises making a positive transparency from said negative, opaquing on said positive all tone values except white, making from said opaque positive a block-out negative in which the white areas of the subject are opaque and'all other areas are transparent, superimposing said negatives in register with one another, and making, by means of light transmitted through said superimposed negatives, a positive which is clear in its white areas and has tone values in its other areas.

2. The process of making a set of white-corrected positives for the production of color printing-plates which comprises producing a set of color-separation negatives representing the individual colors required to reproduce the original subject, making a positive from one of-said negatives, opaquing in on said positive all tones other than white-but leaving the areas representing the whites transparent, making from said opaqued positive a block-out'negative in which the areas representing the whites are opaque and all other areas are transparent, superimposing said blockout negative in turn on and in register with each of said color-separation negatives, and producing by light transmitted therethrough a set of whitecorrected color-separation positives which are entirely clear or transparent in the white areas and have tone values in all other areas.

3. The process of making a set of white-corrected positives for the production of color printing-plates which comprises producing a set of colon-separation negatives representing the individual colors required to reproduce the original subject, making a positive from one of said negatives, opaquing in on said positive all tones other than white but leaving the areas representing the whites transparent, making from said opaqued positive a block-out negative in which the areas representing the whites are opaque and all other areas are transparent, superimposing said blockout negative in turn on and in register with each of said color-separation negatives, and photographing the same through a half-tone screen by light transmitted through said negatives to produce a set of white-corrected color-separation half-tone positives which are free from dots in the white areas and have tone values in the remaining areas.

WILLIAM J. WILKINSON. 

